1. Field of the Invention
The present invention relates to a flat display panel for application in a thin display device such as a liquid crystal color TV.
2. Description of Prior Art
Our present Information Age demands quick and accurate access to various information. A personal information display device has drawn attention by promising means for this purpose. Low voltage, power-saving, thin and small information display devices are demanded for personal use. A liquid crystal matrix display panel meets these requirements to some extent. Research and development of the liquid crystal matrix display panel is now under way in various industrial fields, with a particular focus on a liquid crystal color TV.
The matrix display panel for a liquid crystal color TV are of two types: an active matrix type and a simple matrix type. The active matrix display panel comprises a plurality of signal electrodes, a plurality of scanning electrodes arranged in a matrix, and a switching transistor having a liquid crystal-driving electrode being formed in each intersection of the electrodes to constitute a picture element. The switching transistors, driven by external signals, select necessary picture elements, to thereby displaying a picture. Voltage on each liquid crystal-driving electrode is applied to the liquid crystal statistically. In contrast, the simple matrix display panel comprises two glass substrates. One substrate includes a plurality of signal electrodes and the other substrate includes' a plurality of scanning electrodes. The two substrates are superimposed on each other so that the signal electrodes and the scanning electrodes are arranged in a matrix. The picture element in each intersection of the electrodes is driven dynamically. In either matrix panel type, the signal electrodes and scanning electrodes are extended outside the picture element region and connected to the output terminals of LSI chips, respectively. A color filter is indispensable in the panel. Moreover, the panel is required to transmit light and includes a light source such as a fluorescent lamp.
In a typical liquid crystal active matrix color display panel, the conventional liquid crystal display module includes a substrate on which LSI chips for driving the matrix are mounted as described in the following.
FIG. 1 shows an example of the conventional liquid crystal display module. A wiring region with distributing electrodes 14 formed thereon is provided in the peripheral region 13 of the picture element region 12 of a liquid crystal display panel 11, so that liquid crystal-driving LSI chips 15 can be mounted directly on the display panel 11. Input and output leads are connected to the pads 16 of the LSI chips 15 either by wire bonding, TAB or a flip chip bonding method.
In the liquid crystal display module of the above construction, the wiring region and the LSI chip-mounting region are located in the peripheral region 13 of the picture element region of the liquid crystal display panel 11. In addition, the panel 11 must include another region 19 for connection with an external circuit which supplies signals to the LSI chips 15. Consequently, the area of the display panel 11 becomes rather large compared with the area of the picture element region 12. Particularly when the display panel of this type is used in a portable display device having a two to three inch screen, the area occupied by the wiring region, the LSI chip-mounting region and and external circuit-connecting region is obviously large for the screen size. As a larger display panel is used, the number of display panels that can be obtained from a glass substrate sheet of a given size decreases, and a cost increase results. Besides, in a case where numerous LSI chips are loaded, the input signal lines must have a multilayer interconnection, to effect achieve a simpler structure and smaller area of the region for connecting the input signal lines of the LSI chips to the external circuit. This method would, however, sacrifice the yield of the a liquid crystal display module.
A proposed method for removing the above disadvantages uses a flexible substrate on which liquid crystal-driving LSI chips are mounted and the substrate is connected to a liquid crystal display panel by soldering by using thermoplastic anisotropic conductive sheets or is anisotropic conductive rubber connectors. The proposed construction is described in detail below.
FIG. 2 is a plan view of a second example of the conventional liquid crystal matrix display panel, and FIG. 3 is a sectional view taken along the line X-X' of FIG. 2. A flexible substrate 22 with liquid crystal-driving LSI chips 21 loaded thereon is positioned properly with respect to the electrodes on a liquid crystal display panel 23 and the substrate is connected to the panel 23 by soldering. The other end of the flexible substrate 22 is connected by soldering with a -shaped double side printed circuit pc board 24 on which input signal lines (common wiring) are printed.
Because the LSI's 21 are mounted on the flexible substrate 22, the liquid crystal display panel 23 may be of a large enough size to accomodate a picture element region 25 and a joint margin 26 for connection with the flexible substrate 22. Accordingly, the liquid crystal display panel 23 can be made small, resulting in cost reduction. However, because the PC board 24 is placed on the same plane as the liquid crystal display panel 23 as shown in FIG. 3, the entire set size increases with the screen size, a fatal barrier to a portable display device results. In addition, when chip components and controllers requiring shields, as required by LSI chips, are to be mounted on the PC board 24, the PC board 24 must be made larger. Besides, a height restriction exists for the components to be mounted.